1. Technical Field
The present invention relates to an adiponectin production enhancer comprising sericin as an active ingredient, which can enhance production of adiponectin. The present invention also relates to a pharmaceutical preparation and food and drink which comprise the adiponectin production enhancer, and are effective in prevention and amelioration of various diseases caused by reduction of blood adiponectin levels.
2. Background Art
In modern society, a variety of diseases such as obesity, arteriosclerosis, fatty liver and diabetes have been becoming a huge issue. Conventional treatments of these diseases include pharmacotherapies and many therapeutic agents are known. However, taking of medications may involve side effects such as hypertension, hepatopathy, diarrhea, constipation and headaches, thus, are stressful to patients. In recent years, many approaches for prevention and amelioration of obesity, arteriosclerosis, fatty liver and diabetes have been attempted via dietary habit. Examples of such attempts include intakes of lipolytic agents and dietary fibers, nevertheless, demands for more effective approaches still exist.
Adiponectin is a protein specifically secreted from adipose cells and has been appeared to be closely related to diseases such as obesity, arteriosclerosis, fatty liver and diabetes. Indeed, reduction of blood adiponectin levels in patients suffering from obesity and/or diabetes has been reported (Ouchi, N. et al, Circulation, vol. 100, p. 2473-2476, 1999; and Arita, Y. et al, Biochemical and Biophysical Research Communications, vol. 257, p. 79-83, 1999).
It has also been medically demonstrated that increases of blood adiponectin level ameliorate lifestyle-related diseases such as diabetes (Maeda N. et al., Molecular Medicine, vol. 42, no. 1, p. 11-21, 2005).
Therefore, for the purposes of prevention and/or amelioration of obesity, arteriosclerosis, fatty liver and diabetes, a functional component capable of increasing blood adiponectin level with no or little side effect is desired.
A soybean protein, for example, is known as one of such functional components (Nagasawa et al., Horm. Merab. Res., 34, 635-639, 2002). However, this was not estimated to provide sufficient effect. Extracts from Cordyceps Sinensis Saccardo by hot water (Japanese Patent Application Laid-Open Publication No. 2007-31302) and extracts from Amla (Japanese Patent Application Laid-Open Publication No. 2006-56836) are also known as such functional components. Nevertheless, these components have not been tested for their effect on lipid content in liver, hence, the knowledge concerning these compounds with respect to their efficacy in prevention and amelioration of actual disease state such as fatty liver is not yet sufficient. In addition, these materials and active ingredients are not necessarily easy to obtain.
Sericin is a type of silk proteins and have been reported to have various functions and/or effects such as an antioxidant effect (Japanese Patent Application Laid-Open Publication No. H10 (1998)-140154), preventive effect against colon cancer (Japanese Patent Application Laid-Open Publication No. 2000-256210), weight loss enhancing effect, constipation relieving effect and mineral absorption stimulant effect (Japanese Patent Application Laid-Open Publication No. 2000-312568).
However, to the knowledge of the present inventors, there has been no report that sericin has an adiponectin production enhancing effect.